Both companies have strong reputations in the pharmaceutical and healthcare industry. CVS is one of the country’s largest pharmacy benefits managers and a leading retailer with 9,700 retail pharmacies and more than 1,100 walk-in medical clinics. Aetna is one of its oldest and most far-reaching health insurers in the U.S., Reuters reports.

While a merger could help CVS compete even more in fields such as pharmacy benefits, it could encounter antitrust scrutiny given its scale. However, the latest move could also be an essential push to help counteract any effects of an Amazon entrance into the pharmaceutical market after the e-commerce Goliath announced plans to do so earlier this month.

On Thursday, Amazon also received pharmacy-wholesaler licenses in at least a dozen states, sending shockwaves throughout the stock exchange and causing selloffs in shares of McKesson Corp., AmerisourceBergen Corp. and Cardinal Health Inc., Bloomberg reports.

Aetna shares rose more than 11% to $18.48 when news of the potential merger broke Thursday, while CVS shares fell by 3% to $73.31.

Exact terms of the deal are still being negotiated and may surface in the next several weeks.